ITensor/ITensorMPOConstruction.jl: v0.2.0

Zenodo (CERN European Organization for Nuclear Research) · 2026-04-07

What's Changed Allow construction of non-zero flux MPOs. By @corbett5 in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/ Fixed an assembly cutoff resulting in significant increase in one-body accuracy. By @srwhite59 in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/34 Added documentation, and various optimization that sped up construction by over 2x in certain cases. By @corbett5 in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/37 New Contributors @srwhite59 made their first contribution in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/34 Full Changelog: https://github.com/ITensor/ITensorMPOConstruction.jl/compare/v0.1...v0.2.0

ITensor/ITensorMPOConstruction.jl: v0.2.1

Zenodo (CERN European Organization for Nuclear Research) · 2026-04-07

Updated the version in Project.toml Full Changelog: https://github.com/ITensor/ITensorMPOConstruction.jl/compare/v0.2...v0.2.1

ITensor/ITensorMPOConstruction.jl: v0.2.0

Zenodo (CERN European Organization for Nuclear Research) · 2026-04-10

ITensorMPOConstruction v0.2.0 Merged pull requests: Bump codecov/codecov-action from 3 to 4 (#1) (@dependabot[bot]) Moved code to new repo and setup packaging. (#2) (@corbett5) Fix include("graph.jl") (#3) (@mtfishman) CompatHelper: add new compat entry for TimerOutputs at version 0.5, (keep existing compat) (#4) (@github-actions[bot]) CompatHelper: add new compat entry for ITensors at version 0.3, (keep existing compat) (#5) (@github-actions[bot]) CompatHelper: add new compat entry for Memoize at version 0.4, (keep existing compat) (#6) (@github-actions[bot]) Filled out the README. (#7) (@corbett5) Updated README. (#8) (@corbett5) Corbett/types and docs (#9) (@corbett5) Bump julia-actions/setup-julia from 1 to 2 (#10) (@dependabot[bot]) CompatHelper: bump compat for ITensors to 0.4, (keep existing compat) (#11) (@github-actions[bot]) CompatHelper: bump compat for ITensors to 0.5, (keep existing compat) (#12) (@github-actions[bot]) Bump julia-actions/cache from 1 to 2 (#13) (@dependabot[bot]) CompatHelper: bump compat for ITensors to 0.6, (keep existing compat) (#14) (@github-actions[bot]) Start using ITensorMPS.jl (#15) (@mtfishman) CompatHelper: bump compat for ITensorMPS to 0.2, (keep existing compat) (#16) (@github-actions[bot]) Corbett/set scalar bug (#20) (@corbett5) Corbett/formatting (#21) (@corbett5) CompatHelper: bump compat for ITensors to 0.7, (keep existing compat) (#23) (@github-actions[bot]) Bump codecov/codecov-action from 4 to 5 (#24) (@dependabot[bot]) Updated ITensorMPS to 0.3 and ITensors to 0.9 (#27) (@corbett5) Corbett/one large graph left (#28) (@corbett5) Updated docs with block2 comparison. (#30) (@corbett5) Allow construction of non-zero flux MPOs. (#32) (@corbett5) Bump actions/checkout from 4 to 6 (#33) (@dependabot[bot]) Fix MPO_new assembly cutoff and add H1 accuracy regression test (#34) (@srwhite59) Bump julia-actions/cache from 2 to 3 (#35) (@dependabot[bot]) Bump codecov/codecov-action from 5 to 6 (#36) (@dependabot[bot]) Documentation (#37) (@corbett5) Added compat. (#38) (@corbett5) Closed issues: Follow style guides for casing of function names and keyword arguments (#17) Report a bug of ITensorMPOConstruction (#19)

Competing states in the $S=1/2$ triangular-lattice $J_1$-$J_2$ Heisenberg model: a dynamical density-matrix renormalization group study

arXiv (Cornell University) · 2026-02-16

Previous studies of the $S=1/2$ triangular-lattice $J_1$--$J_2$ Heisenberg antiferromagnet have inferred the existence of a non-magnetic ground-state phase for an intermediate range of $J_2$, but disagree concerning whether it is a gapped $\mathbb{Z}_2$ quantum spin liquid (QSL), a gapless (Dirac) QSL, or a weakly symmetry-broken phase. Using an improved dynamical density-matrix renormalization group method, we investigate the relevant intermediate $J_2$ regime for cylinders with circumferences from 6 to 9. Depending on the initial state and boundary conditions, we find two {\it distinct} variational states. The higher energy state is consistent with a Dirac QSL. In the lower-energy state, both the static and dynamical properties are qualitatively similar to the magnetically ordered state at $J_2=0$, suggestive of either a weakly magnetically ordered non-QSL or a gapped QSL proximate to a continuous transition to such an ordered state.

Site basis excitation Ansatz for matrix product states

SciPost Physics Core · 2026-04-08

We introduce a simple and efficient variation of the tangent-space excitation Ansatz used to compute elementary excitation spectra of one-dimensional quantum lattice systems using matrix product states (MPS). A small basis for the excitation tensors is formed based on a single diagonalization analogous to a single site DMRG step but for multiple states. Once overlap and Hamiltonian matrix elements are found, obtaining the excitation for any momentum only requires diagonalization of a tiny matrix, akin to a non-orthogonal band-theory diagonalization. The approach is based on an infinite MPS description of the ground state, and we introduce an extremely simple alternative to variational uniform matrix product states (VUMPS) based on finite system DMRG. For the S=1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>S</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:math> Heisenberg chain, our method—site basis excitation Ansatz (SBEA)—efficiently produces the one-magnon dispersion with high accuracy. We also examine the role of MPS gauge choices, finding that not imposing a gauge condition—leaving the basis nonorthogonal—is crucial for the approach, whereas imposing a left-orthonormal gauge (as in prior work) severely hampers convergence. We also show how one can construct Wannier excitations, analogous to the Wannier functions of band theory, where one Wannier excitation, translated to all sites, can reconstruct the single magnon modes exactly for all momenta.

Competing states in the $S=1/2$ triangular-lattice $J_1$-$J_2$ Heisenberg model: a dynamical density-matrix renormalization group study

Open MIND · 2026-02-16

Previous studies of the $S=1/2$ triangular-lattice $J_1$--$J_2$ Heisenberg antiferromagnet have inferred the existence of a non-magnetic ground-state phase for an intermediate range of $J_2$, but disagree concerning whether it is a gapped $\mathbb{Z}_2$ quantum spin liquid (QSL), a gapless (Dirac) QSL, or a weakly symmetry-broken phase. Using an improved dynamical density-matrix renormalization group method, we investigate the relevant intermediate $J_2$ regime for cylinders with circumferences from 6 to 9. Depending on the initial state and boundary conditions, we find two {\it distinct} variational states. The higher energy state is consistent with a Dirac QSL. In the lower-energy state, both the static and dynamical properties are qualitatively similar to the magnetically ordered state at $J_2=0$, suggestive of either a weakly magnetically ordered non-QSL or a gapped QSL proximate to a continuous transition to such an ordered state.

Quantum Hall to chiral spin liquid transition in a triangular lattice Hofstadter-Hubbard model

Physical review. B./Physical review. B · 2026-01-20

Quantum Hall to chiral spin liquid transition in a triangular lattice Hofstadter-Hubbard model

Physical review. B./Physical review. B · 2026-01-20

We investigate the weak interaction integer quantum Hall (IQH) phase, the intermediate interaction phase identified as a chiral spin liquid (CSL) and the transition between them in the triangular lattice Hofstadter-Hubbard model at a density of one electron per site in an orbital magnetic field corresponding to one-quarter flux per plaquette. Our primary tool is the finite system density matrix renormalization group (DMRG) method with both interaction-strength scan and fixed interaction techniques for cylinders of circumference 3, 5, and 7 and lengths up to 240. For the IQH phase, we use single particle exact diagonalization to clarify finite size effects, including an excess charge on the edges of our cylinders, and the limitations of entanglement spectra degeneracies on small circumference cylinders. For both phases, we use DMRG to study the entanglement spectra, the entanglement entropy, and the effect of flux insertion on charge and spin pumping, all of which show key differences between the two phases. To study the transition, we use interaction-strength scans extending between the two phases, and apply a scaling data collapse of a bond-dimerization order parameter to extract critical exponents. We also extract critical behavior from the divergence of correlation lengths on the IQH side, measuring decay away from edges of both the dimerization order parameter and transverse edge currents. The critical behavior and exponents are consistent with an Ising transition in 1+1 dimensions. Finally, we obtain excited states in various quantum number sectors finding that the gap to a charge neutral momentum $π$ excitation corresponding to fluctuations of the dimerization order parameter closes in the vicinity of the critical point but gaps to other excitations remain large.

ITensor/ITensorMPOConstruction.jl: v0.2

Zenodo (CERN European Organization for Nuclear Research) · 2026-04-07

What's Changed Allow construction of non-zero flux MPOs. By @corbett5 in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/32 Fixed an assembly cutoff resulting in significant increase in one-body accuracy. By @srwhite59 in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/34 Added documentation, and various optimization that sped up construction by over 2x in certain cases. By @corbett5 in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/37 New Contributors @srwhite59 made their first contribution in https://github.com/ITensor/ITensorMPOConstruction.jl/pull/34 Full Changelog: https://github.com/ITensor/ITensorMPOConstruction.jl/compare/v0.1...v0.2

Strong Correlation DMRG and DFT

2025-09-08

This project developed new ways to improve computer simulations of materials where electrons interact strongly with each other, a challenge for today’s most widely used method, density functional theory (DFT). We used an exact numerical method, the density matrix renormalization group (DMRG), to create highly accurate reference results for simple model systems, and used these to test DFT, prove when it will converge, and even train machine-learned functionals. We also invented new kinds of localized basis functions (“gausslets” and “multi-sliced gausslets”) and a “sliced-basis” approach that make high-accuracy simulations faster and more practical. These methods were applied to extended hydrogen systems, enabling the direct derivation of accurate low-energy models from first-principles calculations. We also introduced a new formalism, Conditional-Probability DFT, which could bypass traditional approximations. The tools and results from this work, including open-source software releases, will help scientists design and understand complex quantum materials.